Pesticide transfer from substrate to Hermetia illucens and Tenebrio molitor larvae and impact of fasting on residue contents

Insect farming is increasingly recognized as a solution for sustainable food and feed production. However, use of food waste containing commercially produced fruit and vegetable peels as insect feed ingredients raises safety concerns due to potential pesticide contamination. We examined the transfer of pesticides from feed substrates to black soldier fly larvae (BSFL, Hermetia illucens (L.)) and yellow mealworms ( Tenebrio molitor (L.)), and retention during fasting. To investigate effects of substrate pesticide and concentration on the transfer to larvae, we reared larvae on substrates spiked with three concentrations of the three pesticides boscalid, fluopyram, or etofenprox. Pesticide concentrations in BSFL were less than 10% of substrate concentrations, while mealworms retained up to 27% of substrate concentrations. Etofenprox had highest retention in both species. The total mass of BSFL produced was significantly lower when larvae were reared on substrates containing fluopyram or etofenprox, and a negative concentration-dependent effect was shown for etofenprox. In contrast, mealworm growth was unaffected by pesticides. To investigate fasting effects, we used a mixture of all three pesticides and tested larval contents after 0, 12, 24, 48 and 72 hours. In BSFL, most residues were eliminated within 24 hours, while mealworms required up to 72 hours to achieve similar reductions. Our findings indicate that pesticide transfer from substrate to BSFL and mealworms is species-specific but limited, and that subsequent fasting can serve as an effective post-harvest strategy to reduce pesticide residues. This may facilitate the use of waste from conventionally produced fruits and vegetables in insect farming.